1. Field of the Invention
The present invention relates to a liquid crystal display device having a function of temperature maintenance.
2. Discussion of the Related Art
With the rapid growth of the information age, displays for processing and displaying information have been developed. Further, to meet current demand for a slim profile, light weight, and low power consumption, flat panel display devices have emerged. Accordingly, a thin film transistor-liquid crystal display device (hereinafter, referred to as a TFT-LCD) having excellent color reproduction capability and slim profile has been developed.
In the LCD, liquid crystal cells are arranged on a liquid crystal panel in matrix form. Light transmittance of the liquid crystal cells are controlled using video data signals provided thereto. Images corresponding to the data signals are displayed on the liquid crystal panel.
Generally, the LCD includes a first substrate (e.g., a TFT substrate) and a second substrate (e.g., a color filter substrate), which are opposite to each other and spaced apart from each other by a predetermined distance. The first substrate includes gate bus lines and data bus lines, which are formed in an inner surface of a transparent substrate in matrix form. Further, TFTs acting as switching elements are formed at crossings between the gate bus lines and the data bus lines, and pixel electrodes connected to drain electrodes of the TFTs are formed at regions defined by the gate lines and the data bus lines.
The second substrate is opposite to the first substrate on which a plurality of pixel electrodes is formed. The second substrate includes a black matrix (BM), a color filter layer, and a common electrode on an inner side of the second substrate.
In the above-described LCD, if one gate bus line and one data bus line are selected and a predetermined voltage is applied thereto, a TFT to which the predetermined voltage is applied is turned on and charges are accumulated at a pixel electrode connected to a drain electrode of the turned-on TFT, so that the arrangement of liquid crystals between the common electrode and the pixel electrode is changed.
The change of arrangement is the basis of operation of the LCD. When an electric field is applied between the two substrates, a twist angle is varied depending on the strength of the electric field and a degree of light transmittance is varied.
In particular, liquid crystal is the most important material used in the LCD and can be used in the range of −40° C. to 90° C. The properties of liquid crystal may fluctuate greatly depending on temperature.
FIG. 1 is a plan view schematically illustrating the LCD according to the related art. As shown in FIG. 1, the LCD of the related art includes a liquid crystal panel 10 in which liquid crystals are injected between two substrates and a drive unit 11 disposed at an outer periphery of the liquid crystal panel 10, for driving the liquid crystal panel 10.
The liquid crystal panel 10 includes pixels arranged between two transparent substrates in matrix form and a switching element (i.e., a TFT) for controlling a signal provided to each of the pixels. Further, a conductive layer 25 is formed at an outer periphery of a seal pattern 13 of the liquid crystal panel 10.
Meanwhile, the drive unit 11 includes a printed circuit board (PCB) on which parts for generating various control signals and data signal are mounted and a drive integrated circuit 12 connected with the liquid crystal panel 10 and the PCB, for applying signals to lines of the liquid crystal panel 10.
Further, the LCD is classified as a chip on glass (COG), a tape carrier package (TCP), and a chip on film (COF) depending on the method for packaging the drive circuit 12 in the liquid crystal panel 10. For example, FIG. 1 illustrates the drive circuit 12 packaged in the liquid crystal panel 10 using the TCP.
FIG. 2 illustrates a cross-sectional view of a region A of FIG. 1. As shown in FIG. 2, the LCD includes a first substrate 21 where TFTs acting as switching elements are formed at crossings between gate lines and data lines and a second substrate 27 facing the first substrate 21 and having a black matrix (BM)/color filter layer 26 and a common electrode 24 on a transparent substrate 22. The LCD further includes a conductive layer 25 formed at an outer periphery between the first and second substrates 21 and 27 and a common electrode voltage line 23 formed on the first substrate 21 and electrically connected with the conductive layer 25.
That is, the conductive layer 25 is formed at the outer peripheral portion between the first and second substrates 21 and 27, and the conductive layer 25 is between the common electrode voltage line 23 and the common electrode 24.
If the common electrode 24 and the common electrode voltage line 23 are electrically connected, the temperature can rise.
However, the increase in temperature due to the conductive layer has limitations. Such limitations may change the operational characteristics of the liquid crystals sensitive to the change in temperature and may cause degradation in an image quality.